This invention relates generally to color video processing circuits and specifically to a luminance clipper in a color video processing circuit for clipping super white signals, that is, signals in excess of 100 IRE units, without affecting color.
In many applications it is necessary to prevent peak white signals, which may be produced from a variety of sources, most notably noise, from causing interference in color video processing circuits. A special problem occurs where a baseband color video signal including luminance information, a color subcarrier and such a peak white noise signal is to be applied to a modulator. The peak white signal overloads the modulator and results in a very disturbing audio buzz. The condition is often encountered with satellite receivers where the composite color video signal from the satellite is remodulated and applied to a cable television system, for example. The condition may also occur in some video cassette recorders where signals including color and luminance information are remodulated to other television carrier frequencies,
A common prior art circuit includes an expensive comb filter to separate the luminance signal components from the chrominance signal components, a clipper to clip the luminance signal components to a desired level and an adder for recombining the chrominance signal components and the clipped luminance signal components. That circuit obviates distortion of the chrominance signal components that would occur if the combined luminance and chrominance signal components were clipped.
Another prior art circuit applies the combined luminance and chrominance signal components to a circuit having two branches, one including a color bandpass filter and the other including a 3.58 MHz color trap, the outputs of both branches being recombined in an adder. This circuit is also expensive in that it includes a bandpass filter, a trap and an adder, but has the additional undesirable attribute that all of the luminance signal components are degraded since they must pass through the 3.58 MHz color trap.
As will be seen, the circuit of the invention provides a very simple low cost alternative for accomplishing the same function, that is, for clipping the luminance signal components in a composite color video signal at a predetermined threshold level while having substantially no effect on the passage of the color signal components.